Inhibiting oxidation



Patented Aug. 30, 1949 2,480,450 INHIBITING oxms'rron Robert Cocroit and Elmer W. Brennan, Chicago, and Allan Manteui'fel, Desplalnes, 111., asslgnors to The Pure Oil Company, Chicago, 111., a corporation of Ohio No Drawing. Application July 19, 1945, Serial No. 606,020

13 Claims. 1

This invention relates to oxidation inhibitors and to compositions containing the same.

It is well-known to add small amounts of various additives to hydrocarbon lubricating oils in order to lessen the corrosive effect of such oils on automotive engine bearings and to inhibit oxidation of such oils with the formation at sludge and varnish. Among compounds which have been suggested for this purpose are p,p'-bis- (dimethylamino) -diphenylmethane and p,p'-bis- (dimethylamino) -triphenylmethane.

We have discovered that the effectiveness of compounds of the type above referred to in inhibiting oxidation of oxidizable lubricating liquids can be further improved as oxidation inhibitors and particularly with respect to inhibiting varnish formation by incorporating in the compound a heterocyclic ring attached to the central carbon atom of the molecule.

In accordance with our invention there is added to conventional hydrocarbon lubricating oils or to other compositions which are susceptible to undesirable oxidation in storage or during use, from approximately .01% or less up to 5% by Weight, and preferably approximately 0.1 to 1% by weight 01' a compound having the following formula:

wherein A and A are selected from the group consisting of amino, monoalkyl amino and dialkyi amino radicals, R is selected from the group consisting of hydrogen and a phenyl radical containing a substituent from the group consisting of amino, monoalkyi amino and dialkyl amino substituents in the position para to the central carbon atom of the molecule, and R is a heterocyclic ring attached to the central carbon atom of the molecule by a carbon to carbon linkage.

As specific examples of compounds falling within the scope oi the invention are:

BisA-i-dimetliyl-aminophenyD-2-lurylmethane (cnomQfiQ-monm Bis-(i-dimethyl-amlnophenyl)-2-thicnylmethanc I wmmQfiQ-monm Bis-(Mimethyl-aminophenyD-Z-pyfldyl methane H-N a L (cams lk-Q-MGH.

Bis-(i-dlmethyl-amlnophenyD-Z-tbiazolyl-methane] Compounds in accordance with our invention may be added to the mineral lubricating oil in amounts hereinbefore specified and thoroughly mixed with the oil; or the compounds in the form of concentrates, as for example, dissolved in a portion of the lubricating oil, may be blended with the mineral oil in the engine.

In order to demonstrate the effectiveness of compounds falling within the scope of our invention in inhibiting oxidation of mineral lubricating oils and inhibiting bearing corrosion of automotive engines, a series of Underwood tests were made. In one test a Mid-Continent SAE 30 lubricating oil was tested without any additive. In another test 4,4'-bis-(dimethylamino) -diphenyl methane was added to the lubricating oil in amount of 0.5% by weight. This particular additive is a well-known commercial product which is marketed as a lubricating oil oxidation inhibicacao Iron naphthenate was added to some samples tested in order to catalyze the oxidation and accelerate the test.

The results of the test are recorded in Table II.

Tm: It

Davis orvaen absorption tests Minutes Required for so min. Drop In Pressure With Iron Na bthenate at 800 1'. in

Adam" Without lron Napbthonato at g 0.00127 0.01 0.1 W size. by w. by??? as? is is a is? 1 .2:

i th 1 inc -di eny me one I t'lilifitififiyhfm fiophlnyilarmaments 1. 4 2. 80 660 2,480 2,660 2,140 1.070

and at a pressure of ten pounds per square inch 20 The results in Table II again demonstrate the for a period of ten hours. The Underwood test is described in an article entitled Automotive bearing materials and their application," by A. F. Underwood, Journal of Society of Automotive superiority of bis-(4-dimethyl-aminophenyll -2- iurylmethane as an oxidation inhibitor. Its superiority is outstanding in connection with the test of the sample containing 0.12% by weight of Engineers, volume 43, pages 385 to 392, Septem- 5 iron naphthenate. her 1938. Although the specific examples show the het- The results obtained in the tests are tabulated erocyciic ring as a single ring attached to the in the following table. central carbon atom of the molecule at a point TABLE I hour Underwood tests at 325 F.

Loss in 0 Per Cent Increase in Neutralization Bearing rm Viscosity at 130 F. N 0. Adam" Cu-Pb Ag-Cd kjf am. lilHr. in win. up. mm.

iii as 8-3332 as; i-tiii it;(Etiiifiiiltfitfiififi'iififihfia:::::::::::t: III 9Z4 1519 0157 0160 010061 010033 01012; ofom It is apparent from the results in Table I that not only did bis-( i-dimethyl-aminophenyl)-2- iurylmethane greatly reduce the oxidation of the oil as indicated by the lower increase in viscosity and neutralization number and also greatly decrease hearing loss with respect to both copperlead and silver-cadmium bearings, but this compound was noticeably superior to 4,-i'-bis-(dimethylamino)-diphenyl methane which is regarded as one of the best commercial inhibitors available.

In order to further demonstrate the superior oxidation inhibiting ability of bis-(4-dimethylaminophenyl) -2-furylmethane, oxidation absorption tests in accordance with the modified Davis method were made on a Mid-Continent neutral oil having a viscosity of 500 S. U. S. at 100 F. and on this 011 containing 0.5% of each of the two additives tested and recorded in Table I.

The modified Davis absorption test is based on the method described in Industrial 8: Engineering Chemistry," volume 33, pa e 339 (1941). In the test a ten gram sample is placed in a Bligh flask which is then fllled with oxygen, connected to a U-type manometer and then placed in a constant temperature bath maintained at varione selected temperatures. As oxygen is absorbed by the sample, pressure decreases in the flask and it is recorded at frequent intervals until it has dropped 60 mm. 01' mercury-the practical limit of the apparatus. The time required for the pressure drop of 60 mm. of mercury is taken as a measure or stability or the sample.

alpha to the hetero element, it is to be understood that the heterocyclic ring may be a condensed ring and that it may be attached to the central carbon atom of the molecule by means of a cyclic carbon atom in a Position other than alpha to the hetero elements in the ring.

Although the invention has been described with particular reference to the use of additives in by drocarbon lubricating oils it should be understood that the invention is applicable to use of additives in compositions in general, particularly liquid or semi-liquid, which are susceptible to undesirable oxidation in storage or during use, such as turbine oils, transformer oils, greases, quenching oils and other oils, fats and waxes, both bydrocarbon and non-hydrocarbon in composition.

We claim:

1. A lubricant comprising mineral lubricating oil and a small amount, suilicient to inhibit oxidation of said oil. oi a compound having the formulawherein A and A are selected from the group consisting of amino, monoalkyl amino and dialkyl amino radicals, R is selected from the group consisting of hydrogen and a phenyl radical containing a substituent from the group consisting of amino, monoalkyl amino and dialkyl amino substituents in the position para to the central carbon atom of the molecule, and R is a heterocyclic ring attached to the central carbon atom of the molecule by a carbon to carbon linkage.

2. A lubricant in accordance with claim 1 in which A and A are dimethylamino groups.

3. A lubricant in accordance with claim 1 in which A and A are dimethylamino groups and R is a furyl group.

4. A lubricant in accordance with claim 1 in which the compound is present in the composition in an amount of approximately .01 to 5% by weight.

5. A composition in accordance with claim 1 in which the compound is bis-(4-dimethyl-amlnophenyl) -2-thienylmethane.

6. A composition in accordance with claim 1 in which the compound is bis-(4-dimethyl-aminophenyl) -2-pyridylmethane.

7. A composition in accordance with claim 1 in which the heterocyclic ring is one containing oxygen.

8. A composition in accordance with claim 1 in which the heterocyclic ring is one containing nitrogen.

9. A composition in accordance with claim 1, in which the heterocyclic ring is one containing sulfur.

10. A lubricant comprising mineral lubricating oil, and a small amount, sufficient to inhibit oxidation of said oil, of a compound having the formula (cnmNOi-Omcm,

in which R is a heterocyclic ring attached to the central carbon atom of the molecule by a carbon to carbon linkage.

11. A composition from the group consisting of turbine oil, transformer oils, greases, quenching oils and lubricating oils comprising a mineral oil susceptible to oxidation and a small amount, sufllcient to inhibit oxidation of said 011, of a compound having the formula RI Ih OfjO lh REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Sloan May 7, 1935 Number 

